1. Field of the Invention
The present invention relates to moisture-curable compositions containing (cyclo)aliphatically-bound isocyanate groups and succinyl urea groups, which can be cured in the presence of moisture to form coatings, adhesives and sealants.
2. Description of the Prior Art
It is known that polyisocyanate resins are curable in the presence of atmospheric moisture to form polyurea coatings. During the curing mechanism an isocyanate group reacts with moisture to form an amino group, which then reacts with another isocyanate group to form a urea group. One of the disadvantages of these moisture-curable resins is that the curing mechanism is relatively slow.
It has been suggested in U.S. Pat. Nos. 3,420,800 and 3,567,692 that the curing rate of moisture-curable polyisocyanates can be increased by incorporating either aldimines or ketimines. It is stated that the reaction of moisture with an aldimine or ketimine to form the corresponding amine is faster than the reaction of moisture with an isocyanate group to form an amine. A disadvantage of the use of aldimines and ketimines to accelerate the cure of polyisocyanates is that it requires the preparation of an additional component and requires some type of metering equipment to ensure that the two components are blended in the proper proportions.
It is an object of the present invention to increase the curing rate of moisture-curable polyisocyanates without the need for a co-reactant.
This object may be achieved with the compositions according to the present invention which contain isocyanate groups and succinyl urea groups as described hereinafter. The succinyl urea groups may be formed by the reaction of isocyanate groups with aspartate groups.
Copending applications, U.S. Ser. No. 09/172,751, now U.S. Pat. No. 6,005,047 and Ser. No. 09/172,584, disclose polyisocyanates that have been modified to contain alkoxysilane groups incorporated through amino or aspartate groups in order to improve the cure rate of the polyisocyanates. It is disclosed that the faster curing rates are surprising because alkoxysilane groups, which are also curable in the presence of moisture, cure more slowly than polyisocyanates. However, when both isocyanate groups and alkoxysilane groups are present, a faster curing rate is obtained.